Management of Epicardial and Transvenous Pacing for Adult Patients

Background

Epicardial and transvenous pacing are temporary methods of supporting bradycardia, bradyarrhythmias and tachyarrhythmias until resolution or definitive treatment is completed, typically by permanent pacemaker insertion.

In the initial emergency management of bradycardia, pharmacological agents are usually sufficient. However, in peri-arrest or cardiac arrest patients where this is insufficient and epicardial/transvenous pacing wires are not already in situ, non-invasive transcutaneous pacing is recommended as a temporary measure whilst more definitive temporary transvenous pacing is urgently organised.

Indications for Temporary Cardiac Pacing

Historical Context

Temporary epicardial wires have been used since the 1960s for intra- and post-operative management of bradycardia, bradyarrhythmias, and tachyarrhythmias in cardiac surgery (Khorsandi et al., 2012).

Types of Temporary Cardiac Pacing Wires

Epicardial Temporary Pacing Wires

Description

• Material: Thin stainless-steel wires insulated with Teflon
• Insertion: Sutured to epicardial surface of right atrium or right ventricle with dissolvable sutures during cardiac surgery
• Wire types: Atrial, ventricular, or both may be inserted
  • If only one set present: Always ventricular
• Wire location identification:
  • Ventricular wires: Emerge on LEFT of sternum (usually white)
  • Atrial wires: Emerge on RIGHT of sternum (usually blue)
• System types: Unipolar or bipolar

Unipolar vs Bipolar Systems

Duration of Effectiveness

Transvenous Cardiac Pacing Wires

Transvenous temporary cardiac pacing provides life-saving emergency therapy for patients with bradycardia and arrhythmias causing haemodynamic instability. It can be used as a bridging technique when permanent pacemaker insertion is not immediately indicated or available (Tjong et al., 2019).

Insertion Procedure

1. Bipolar single temporary transvenous catheter floated under fluoroscopic guidance through right heart whilst ECG monitored
2. Wire with deflated balloon passes through:
   • Right atrium
   • Tricuspid annulus
   • Right ventricle (tip pointing down into apex)
3. Balloon inflated:
   • Sits against right ventricular wall
   • Protects from damage
   • Keeps in place during deep inspiration
4. Placement confirmed by:
   • Chest X-ray
   • Successful pacing attempt

Electrocardiographic Features

The Pulse Generator (Pacing Box)

The pulse generator (commonly called "pacing box" in clinical practice) is battery-operated and attached to epicardial or transvenous pacing wires, supplying them with electrical current. Several companies manufacture pulse generators, but basic important functions are similar across devices.

Key Functions

The pulse generator allows adjustment of:

• Pacing mode
• Pacing rate
• Pacing output
• Sensitivity to intrinsic activity

Understanding Cardiac Pacing

1. Pacing Mode

Mode Selection Options

Pacing modes are selected on the pulse generator by the operator. One of the following two modes is selected:

Single Chamber Modes

If pacing wires lead to only a single chamber (atrium or ventricle):

Dual Chamber Pacing Modes

In dual chamber modes, pacing wires must be present in both atrial and ventricular chambers. Can use single chamber modes OR:

• DDD (Dual chamber demand pacing)
• DOO (AV sequential asynchronous pacing)
• DVI (AV sequential, ventricular inhibited)
• DDI (AV sequential, non-P-synchronous, with dual chamber sensing)

British Pacing and Electrophysiology Group (BPEG) Code

This standard code helps interpret pacing mode settings:

Detailed Mode Descriptions

2. Pacing Rate

Relationship to Cardiac Output

Setting the pulse rate (beats per minute) on the pulse generator controls cardiac output:

• Cardiac Output = Heart Rate × Stroke Volume
• As heart rate increases beyond optimal point: stroke volume falls → cardiac output decreases
• Each patient has an optimal heart rate for cardiac output
• Increased heart rate comes at expense of increased oxygen consumption

Back-up Rate

A back-up rate can be set (determined by operator, normally around 50 bpm, but some patients may require higher).

Purpose: For patients transitioning to reliance on intrinsic rhythm, provides safety backup:

• Patient remains in own intrinsic rate and rhythm until heart rate decreases below set backup rate (e.g., 50 bpm)
• If patient becomes haemodynamically compromised, backup rate triggered

3. Output

Mechanism

• Energy delivered in brief burst over ~0.6 milliseconds
• Pulse generator discharges capacitor into leads
• Electricity briefly stored in pacing leads
• Voltage between electrodes increases suddenly to 5V
• Voltage then decreases over short period (determined by lead impedance)
• Impedance: Opposition to alternating current given by effect of resistance and reactance in circuit

Capture

Capture Threshold

Importance:

• Higher output and current → more rapid wire encrustation → reduced effectiveness
• Important to keep output current as low as safely possible (Yartsev, 2020)
• Monitor for occasional missed beats → rising capture threshold → requires output increase

Finding the Capture Threshold

1. Set pulse generator rate well above intrinsic rate (chamber continuously paced)
2. Start reducing output until QRS no longer follows each pacing spike
3. The minimum output at which there is still consistent capture = capture threshold
4. Set output at twice the capture threshold (margin of safety)
   • If electrodes become encrusted, will still continue to pace successfully

4. Sensitivity

Key Concepts

Problems with Sensitivity Settings

• Too low sensitivity (too sensitive): Inappropriate sensing of signals including R-on-T waves → inappropriate prevention of pacing
• Important limitation: If no significant underlying rhythm, NOT possible to assess electrode sensitivity

Checking Sensitivity Threshold

1. Put pulse generator in VVI or DDD mode (intrinsic activity should inhibit pulse generator)
2. Change rate to lower than patient's intrinsic rate
3. Change output to minimum setting (capture not required, only pacing indicator LED)
4. Observe sense indicator
5. Increase mV dial (decreases sensitivity)
6. Eventually sensitivity will be so low that intrinsic electrical activity no longer sensed
   • Pacemaker unable to detect electrical activity
   • Patient paced at set rate (flashing pacing indicator LED)
7. Decrease mV dial (increases sensitivity)
8. Eventually reach sensitivity value where pacemaker senses every P-wave or QRS interval
9. This sensitivity value = sensitivity threshold
10. Set sensitivity at half to one-third of sensitivity threshold

Setting Sensitivity Using Osypka Pace 203H

The Osypka Pace 203H pulse generator can identify amplitude of native P and R waves:

1. Press "Pause" button
2. Observe lower screen for P wave and R wave amplitude
3. Set Atrial sensitivity to 1/3 P wave amplitude or as low as it will go, whichever is higher
   • Only relevant in atrial or dual pacing mode
4. Set Ventricular sensitivity to 1/3 R wave amplitude or as low as it will go, whichever is higher
5. If in doubt: set sensitivity to as low as it will go and seek senior help

5. Assessing the Underlying Rhythm

Procedure:

• Turn down pacing rate slowly until underlying rhythm revealed and can be assessed
• May not be possible to identify underlying rhythm if haemodynamic instability when pacing rate reduced below intrinsic rate
• 12-lead ECG may be completed if patient has stable underlying rhythm

Setting the Pulse Generator with Back-up Rate

Daily Nursing Care

Registered nurses caring for patients with epicardial or transvenous pacing wires should complete the following procedures at the required frequency.

Nursing Procedures Checklist

Daily Medical Care

The medical team caring for patients with epicardial or transvenous pacing wires should complete the following checks at the required frequency and document in the patient record. Checks should be performed by member of medical team trained to perform pacing checks or pacing technicians.

Emergency Procedures

This section provides detailed emergency protocols for managing pacing complications.

Emergency Set-up of VVI Pacing

Loss of Paced Rhythm

Safety Considerations

Magnetic Resonance Imaging (MRI) and Computerised Tomography (CT)

Pacing Wire Storage and Environmental Safety

Minimum Monitoring Requirements

• Continuous ECG monitoring with pacing monitoring activated
• Monitor for:
  • Temporary pacing failure
  • Associated arrhythmias
• Immediate access to defibrillator with transcutaneous pacing capability essential

Wire Handling and Storage

Removal of Epicardial Pacing Wires

Transitioning to Permanent Pacemaker

Patients receiving temporary pacing through epicardial or transvenous wires may remain pacing-dependent, requiring insertion of permanent pacemaker. Timing of insertion determined by clinical course.

Wire Lifespan

• Epicardial wires: Often begin to fail after 4-5 days
• Transvenous wires: May be effective for longer (Reade, 2007)

Pre-insertion Requirements

References

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